According to Sidit77, it’s necessary for the Raspberry Pi used in this project to be configured as a USB input device. He’s using a Pi Zero W but a Raspberry Pi 4 would also work. The project uses a custom UDP to provide low-latency and better overall performance.
When testing the final product, Sidit77 confirmed that various keyboard layouts appear to translate correctly and all the mouse buttons work along with the scroll wheel. Switching between machines requires no external button, just a hotkey.